There is known a battery cell configured such that a positive electrode and a negative electrode are laminated with a separator interposed therebetween. As a battery module including this kind of battery cell, there is known a battery module in which the battery cell is contained in a module case for protecting the battery cell.
By the way, in the battery module, when an internal short-circuit occurs in the battery cell, gas is generated in the battery cell, and the internal pressure of the battery cell rises. When the internal pressure rises, the battery cell expands in the thickness direction of the battery cell, which is the direction in which the positive and negative electrodes are laminated with the separator disposed therebetween. In cases where the above described battery cell, which is contained in the module case, is unable to expand, there is a gradual increase in the cell's internal current, which results in the generation of heat and the battery cell is consequently ruptured.
As a measure to enable a battery cell to expand, Patent Document 1 discloses a configuration in which a deformation member for facilitating the expansion of the battery cell is disposed in a module case containing battery cells.
The module case included in the battery module described in Patent Document 1 contains the deformation member, together with the battery cells. The module case is configured so as to allow expansion and to press the battery cell which expands, by the deformation member. When the deformation member is pressurized at a pressure which is a predetermined value or less, it elastically deforms, and when it is pressurized at a pressure which is more than the predetermined value, it does not deform anymore.